Structure of the solid phases of SiH4

X-ray studies of polycrystalline samples of monosilane SiH4 are done in the existence regions of the low-temperature and high-temperature phases with the use of photometric and diffractometric methods. It is found that the unit cells of both phases have monoclinic symmetry. The phase transition from the low-to the high-temperature phase is accompanied by an appreciable volume jump Delta V/V=1.9% and a change of the number of molecules in the cell from 4 to 32. The unit cell in the low-temperature phase (at T=6 K) has parameters a=8.198 +/- 0.002 angstrom, b=4.601 +/- 0.001 angstrom, c=7.364 +/- 0.002 angstrom, beta=90.32 +/- 0.08 degrees, volume V=41.85 cm(3)/mole, and density 0.78 +/- 0.05 g/cm(3). The high-temperature phase is substantially orientationally disordered, containing Z=32 molecules per cell and has the parameters a=13.660 +/- 0.003 angstrom, b=12.767 +/- 0.003 angstrom, c=13.333 +/- 0.003 angstrom, beta=93.66 +/- 0.06 degrees, volume V=43.67 cm(3)/mole, and density 0.735 g/cm(3) at T=65 K. The structural and a number of physical characteristics of silane are compared with the corresponding properties of other crystals made up of tetrahedral molecules. (C) 2008 American Institute of Physics.